1. Field of the Invention
The present invention relates to a position-sensorless motor control device that drives and controls a motor without the use of a rotor position sensor. The present invention also relates to a motor drive system incorporating such a position-sensorless motor control device.
2. Description of Related Art
There have conventionally been developed techniques for detecting the rotor position of a motor without the use of a sensor. Some of such techniques propose to exploit injection of a high-frequency rotation voltage or a high-frequency rotation current.
For example, JP-A-2003-219682 discloses a technique according to which a high-frequency rotation voltage is applied to a motor, and the rotor position thereof is estimated based on the major-axis direction of the ellipse described by the current vector locus. JP-A-2004-80986 discloses a technique according to which a high-frequency rotation voltage is applied to a motor, and the current that flows therethrough is converted into a current on the α-β axes; then the peak values and the phases of the α-axis and β-axis components of this current are detected to find the angle of the ellipse major axis (d axis) from the α axis.
JP-A-2002-51597 discloses a technique according to which the cosine and the sine of the mid-angle between the in-phase magnetic flux vector and the mirror-phase magnetic flux vector of a high-frequency wave are estimated, and these estimated values are used as rotation signals for a vector rotator. JP-A-2003-153582 discloses a technique according to which a mapping between the positive-phase axis and the negative-phase axis is exploited to estimate the rotor position.
Disadvantageously, however, according to any of the techniques disclosed in the documents mentioned above, to obtain a signal based on which the rotor position can be estimated, it is necessary to subject the extracted signals to complicated processing; that is, they enable position-sensorless control indeed, but only through complicated processing.